Up to a quarter of a million adults with mental illnesses are not being supported by an appropriate adult while in police custody, according to a report.

An analysis of police data showed appropriate adults – trained volunteers who help with communication, welfare and legal rights – were used in around 45,000 of the 1.4 million detentions and voluntary interviews of adults each year, even though up to 280,000 involved those who were mentally vulnerable.

The home secretary, Theresa May, who commissioned the report by the National Appropriate Adult Network, said the situation was “not acceptable” and she would review the charity’s recommendations.

Appropriate adult schemes were introduced in the 1980s in response to miscarriages of justice involving vulnerable people, and local authorities have a legal duty to provide them for children.

Of those who completed the survey, around a third said they received no training in identifying vulnerable suspects, while some reported spending hours trying to find a suitable appropriate adult, admitting to sometimes asking random members of the public or proceeding without one.

May said: “Appropriate adults provide vital support and help to demystify what can be a confusing, sometimes frightening, experience in police custody.

It’s time we gave our most vulnerable people proper protection in custody | Chris Bath

Read more

“Evidence suggests there is a lack of appropriate adults to safeguard the welfare and rights of mentally vulnerable adults in police custody. That is why I commissioned this review to determine where the problems lie.

“The status quo is not acceptable and I am concerned that vulnerable adults are not always receiving the support of an appropriate adult. We are currently examining the recommendations and implementation options to ensure that vulnerable people are provided with the support they are entitled to.”

Chris Bath, chief executive of the National Appropriate Adult Network, the charity which led the study, said: “People with learning disabilities, mental ill health, traumatic brain injuries or autistic spectrum disorders are some of the most vulnerable citizens, and state detention is perhaps the most vulnerable situation. We have a moral and a legal duty to ensure appropriate adults are available wherever people live.”

The recommendations in the report include a national framework for the provision of appropriate adults, a statutory duty on police officers to secure one and improvements to police training and record keeping on vulnerable adults.